A090401 Expansion of 1/(1-3x+3x^4).

1, 3, 9, 27, 78, 225, 648, 1863, 5355, 15390, 44226, 127089, 365202, 1049436, 3015630, 8665623, 24901263, 71555481, 205619553, 590861790, 1697881581, 4878978300, 14020076241, 40287643353, 115769285316, 332670921048

Offset

0,2

Links

Table of n, a(n) for n=0..25.

Index entries for linear recurrences with constant coefficients, signature (3,0,0,-3).

Formula

a(n)=3a(n-1)-3a(n-4); a(n)=sum{k=0..floor(n/2), comb(n-3k, k)3^(n-3k) }.

Mathematica

CoefficientList[Series[1/(1-3x+3x^4), {x, 0, 30}], x] (* or *) LinearRecurrence[ {3, 0, 0, -3}, {1, 3, 9, 27}, 30] (* Harvey P. Dale, Apr 19 2015 *)

Crossrefs

Sequence in context: A268013 A269613 A006810 * A181137 A113041 A269650

Adjacent sequences: A090398 A090399 A090400 * A090402 A090403 A090404

Keyword

easy,nonn

Author

Paul Barry, Nov 28 2003

Status

approved